Usually, a DC-DC converter is configured to unidirectionally increase a voltage from a high-side voltage to a low-side voltage or unidirectionally decrease a voltage from a low-side voltage to a high-side voltage.
Vichcles have two direct-current power supply systems each using a battery with a different voltage value (high-side voltage, low-side voltage).
Accordingly, in vehicles which require high efficiency, it has been proposed to bidirectionally convert voltages between two direct-current power supply systems, that is, from a high voltage to a low voltage, or from a high-side voltage to a low-side voltage, and utilize limited energy efficiently.
In order to mutually supply electric power, a bidirectional DC-DC converter has been employed in which a direct-current voltage increase circuit and a direct-current voltage reduction circuit are arranged in parallel between direct-current power supply systems and are used appropriately (for example, see Patent Document 1).    [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2002-165448